The present invention relates to a conductive composition and a bulb for a cathode ray tube (CRT) employing a conductive layer formed of the same, and more particularly, to a conductive composition exhibiting good coating performance and solubility and capable of forming a conductive layer exhibiting enhanced luminance due to little residue left after a sintering process, and a CRT bulb employing a conductive layer formed of the same.
Conductive compositions have been used in various fields applying electrophotographic techniques, such as photocopiers and laser printers, and especially for the phosphor screen of a color cathode ray tube. Here, the phosphor screen used for a color cathode ray tube can be manufactured by a slurry coating method (hereinafter, referred to slurry method) or an electrophotographic process.
In the slurry method, the panel is cleaned and then three phosphor slurries (corresponding to the primary colors, i.e., green, blue and red) are respectively applied to on the panel. Each phosphor slurry contains polyvinylalcohol (as a main component), ammonium dichromate, and one of green-, blue-, and red-emitting phosphors.
In more detail, the first (e.g., green) phosphor slurry is applied to on the inner surface of the panel. The resultant panel is exposed to ultraviolet light and developed, to form a phosphor pattern (dotted or striped) which is then dried to yield the green portion of a final pattern. The same procedure is applied for the blue-emitting phosphor slurry and the red-emitting phosphor slurry, in turn, to thereby complete the phosphor pattern.
The slurry method, however, has some serious problems. First, the phosphors are not completely developed and thus remain at an exposed portion in a relatively large amount so that the remaining phosphor is mixed with the phosphor applied later. Second, a reaction between the polyvinylalcohol and ammonium dichromate contained in the slurry produces a coloring substance, which deteriorates color purity.
On the other hand, another method for manufacturing the phosphor screen of the color cathode ray tube using an electrophotographic technique is not only simpler than the slurry method, but can also provide a color cathode ray tube having better luminance properties. In this method, first, the panel is treated with chemicals and a surfactant, rinsed with distilled water and then dried. Thereafter, a conductive layer is formed on the inner side of the panel by a spin-coating method or spraying method, and a photoconductive layer is then formed thereon. The photoconductive layer is electrified with a corona electrifier and a predetermined portion thereof is exposed through a shadow mask. Finally, the exposed portion of the photoconductive layer is controlled to be in an electrically neutral state, and green-, blue- and red-emitting phosphor compositions are respectively adhered to the unexposed portion thereof, to form a phosphor screen.
In the case of an electrophotographic photocopier, since aluminum cylinder is a conductor, a photoconductive material can be directly applied to the aluminum cylinder for use as a photoconductor. Meanwhile, in the case of a color cathode ray tube of which the front panel is made of insulating material, e.g., glass, the conductive layer should be formed prior to forming a photoconductive layer because the photoconductive material cannot be directly applied to the CRT's glass panel.
However, since a conventional conductive composition such as polybrene-propanol exhibits poor solubility and coating performance, and the conductive layer formed of the conventional conductive composition has a high surface resistance of 10.sup.9 .about.10.sup.11 .OMEGA./.quadrature.. Furthermore, the conventional conductive composition has a poor pyrolysis property and thus generates a large amount of residue during a sintering process. The residue should be removed in order to increase luminance.
Owing to the above-described physical and chemical limitations, the conventional composition is not suitable for the electrophotographic technique.